Video: Exclusive: More revelations from Rowling

Spoiler alert: This story reveals some key plot points in the final Harry Potter book.

It’s hard to imagine that J.K. Rowling would have any regrets about Harry Potter, not after her epic fictional hero delivered her from public assistance, introduced millions of children to the joys of reading and made Rowling one of the most celebrated authors of this or any other generation.

But, she told TODAY co-host Meredith Vieira in an exclusive broadcast interview, she carries one great regret with her always, one that Dumbledore himself would not be able to cure.

She never told her mom about the books.

“She never knew,” Rowling said. “She would have loved this just in the sense any mother wants to know their child is successful. She would have been at every event I did. She would have had so much vicarious pleasure in seeing who I met and what I did. Not telling her, that’s a massive regret.”

Rowling had conceived the entire plot of Harry Potter while on a train trip in 1990. She began writing immediately, but didn’t tell her mother, who died that December at the age of 45 after a 10-year battle with multiple sclerosis.

After her mother’s death, the classically educated Rowling moved to Portugal, where she got a job teaching English as a second language. She married there in 1992 and had a daughter, Jessica. After the brief marriage ended, she returned to Scotland, where she lived on public assistance and wrote “Harry Potter and the Philosopher’s Stone” in local cafes, her daughter sleeping in a pram at her side.

The first book was published in 1997 with an initial press run of 1,000 copies. Rowling’s publisher, Bloomsbury Publishing, told her to get a day job, as children’s books seldom made a great deal of money.

But the rights for the American edition fetched an advance of $105,000 from Scholastic Books, a sum that astonished Rowling.

If her mother never knew the quest her daughter had set out on, a quest that would consume 17 years of her life and make her wealthy and famous beyond her dreams, she still had an enormous affect on the books.

“Mum dying had a profound influence on the books because I had been writing the Harry Potter series, and in the first draft his parents were disposed of really in quite the cavalier fashion,” Rowling told Vieira. “Six months in, my mother died. I really think from that one moment on, death became a central, if not the central, theme of the seven books. How we react to death, how much we fear it. In many ways, all of my characters are defined by their attitude to death.”

Who lives and who dies
And much of the excitement about the final chapter of the epic tale, “Harry Potter and the Deathly Hallows,” has also been defined by speculation about which characters die.

Rowling has been besieged by questions about who lives and who dies. She told Vieira of talking to a young reader who begged her not to kill certain characters, and her heartbreak at knowing that they had already been killed off by her pen. Even her sister looked at her once and said, “If you kill Hagrid, I won’t forgive you.”

But she kept her secrets well. Even Daniel Radcliffe, the actor who plays Harry Potter, had to ask about his character’s fate.

“I took him out to dinner, and at one point during dinner, he leant in and he said, ‘Look, I’ve just gotta ask you. Do I die?’” Rowling said.

“I whispered, so no one else could hear, ‘You get a death scene,’” she said.

“But Dan is very smart. And I’m pretty sure he would have walked away from dinner thinking, ‘Yeah, I get a death scene, but what does that mean? She didn't say, ‘Yes, you die,’ so I hope he's happy.”

Rowling praised the five movies filmed so far, saying that they perfectly capture her vision, and said she wanted to be first in line when Universal Studios, whose parent company is NBC Universal, opens its Harry Potter theme park.

The interview took place in Edinburgh Castle in Scotland, a Hogwarts-like fortress.

At one point, Vieira confessed that one of her favorite scenes in the first book is when the 11-year-old Harry finds the Mirror of Erised, which shows the person looking into it his or her deepest desire.

“There’s something about that, when he looks in the mirror and sees his family, that’s so moving to me. If I had the mirror here and you looked in, what do you think you would see?” Vieira asked.

“I would definitely see what Harry sees. I would have seen my mother,” Rowling said. “I would be able to have a conversation with my mother.”

“Dateline NBC” will air a special hour with the author on Sunday 7 pm/6 pm Central.